Process for fusion of high-melting metals



Feb. 25, 1958 HATHAwAY u; 7 2,824,794

PROCESS FOR FUSION 0F HIGH-MELTING METALS Filed May 18, 1954 1N VEN TOR.

ATTORIVZ Y 2,824,794 PROCESS FOR FUSION OF'HIGH-MELTING METALS Augustus J. Hathaway III, Niagara Falls, N. Y., assignor to National Lead Company, New York, N. Y., a corporation of New Jersey Application May s, 1954, Serial No. 430,615

4 Claims. or. 75-84) This invention relates to the melting or fusion of highmelting metals and is particularly concerned with the fusion of high-melting reactive metals such as titanium and zirconium and alloys of such metals.

Such metals are usually produced as a sponge or in powder form which must be fused eitherto form ingots, that may be converted bymachining, rolling or other known processes into desired articles or shapes, or to l 2 In copending application Serial No. 260,946, filed December 10, 1951, now Patent No. 2,678,887, issued May 18, 1954, of which the present application is in part a continuation, it is disclosed that refractories containing large amounts of calcium oxide and smaller amounts of I both zirconium dioxide and titanium dioxide are highly resistant to hydration and may be satisfactorily used in the fusion-of high melting reactive metals such as titanium, zirconium an'd'alloys of these metals. In such use it has beenfound that the refractories are so resistant to attack 5 by the molten metals that only a relatively slight or insignificant increase inhardness of the metal occurs.

As set forth injthe above mentioned application, such refractories may beformed into crucibles or in other re- Patented Feb. 25, 1958 fractory shapes according to conventional or other known procedures. In many instances it will be found desirable to employ a prefi'red grog, which has been reduced to granularform, in forming crucibles for use in melting titanium, zirconium 'and'the'like. As is well known, the use of a prefired grog materially reduces shrinkage in the formed bodies and also reduces the tendency of the bodies to crack form cast articles. Melting of these reactive metals is,

containers an undesirably large pick-up of carbon is.

likely to occur. When oxide-type refractories are used, the reactive metal picks up not only metallic impurities,

but also, and more importantly, oxygen. It has been' found that even quite small amounts of" oxygen are deleterious as the hardness of the metal is greatly increased thereby. The consequent impairment of working' properties, such as ductility and malleability, may

be so great that working of the metal is difiicult or impossible.

It is therefore'an objectof the present invention to provide a method for fusing high-melting metals and alloys in which contamination of the metal or alloy is minimized.

'Another object of the invention is to provide a method.

for fusing high-melting metals and alloys which results in insignificant or relatively slight increase in hardness,-

of the metal or alloy- A further object of the invention is to provide a method for fusing high-melting metals and alloys which involves the use of a crucible thatis capable of resisting attack. by the molten metals and alloys..

Another object ofthe present invention is to provide during firing. In making crucibles for carrying out the process of the present invention the grog, employed may be o'f any' desired composition and the desired final compositionof, the fired crucible'can be obtained by mixing. 7 withthe grogappropriate quantities ofthe various conf stituents. The grog may. either be merely sintered or, if desired, may be actually fused prior-toreduction to granu1arf0rm. a q

As further pointed out in the copendingapplication referred, to,"in preparing mixes from which crubiles suitable foir carrying out the process of the present invention may belformed, it is possible. to use either the metal oxides as such or substances whichfwhen fired, are converted to the several oxides,'fCaO, ZrO and TiO which are desired in the final product. Thus, for example, calcium carbonate,

calcium hydroxide or calcium nitrate might be usedin the raw mixsince upon heating these materials are .con-. Similarly, for example, the TiC); and 210 may be provided by using rutile, titanium.

verted to calcium oxide.

hydroxideor titanium sulfate forthe former and baddeleyite, zirconium sulfate or hydrated zirconium oxide- (zirconium hydroxide) .for the latter. Calciumzirconatei and/or .calcium-titanate may also be used as ingredients-- since'each ofthese materials is a combination-of two of the oxides desired in the mix. v

a crucible suitable for fusing high-melting, reactive metals without significant increase in the hardness of said metals.

. Other objects and advantages ofthe present invention,-

will; be apparent from the following description taken in conjunction with the accompanying drawings in which:.

Figure 1, is a vertical sectional view through an enclosed furnace which may conveniently be employed in:

the fusion of high-melting metals and alloys in accordance withthe present invention and the casting of ingots thereof;

Figure'2'is a vertical sectional view through a mo dified "form of crucible adapted for carrying out the present invention; and

line 3-3 of Fig re 2,

Figure 3 is a horizontal sectional view taken on the Figure 2 the modified crucible shown in,

In carrying out the invention of thepresent application thehigh-melting metal or alloy is placed in a container or crucible of a CaO--ZrO TiO refractoryand heatedin;

an inert atmosphere 'to fusethe metal. The metal ma-ythen f 1 be permitted to solidify or freeze in the crucible, ,the ingot; resulting being removed from the crucible when the lat-ter has been cooled and taken from the furnace, or, alternatively, the molten metal may be poured into a mold.- The:

fusion is preferably carried out in an inductively heated,- electric furnace. which, of course, must be enclosed to prevent access of air to the molten metal. The furnace enclosure may be evacuated or an atmosphere of-aninert gas 7;

such as argon or helium may be provided therein.

In Figure 1. ofthe drawings there is-shown an apparatus suitable for the fusion of metals such as titanium, zirconium-or alloys thereof and casting of the fused metal or alloy into a mold, all either in vacuum or in an inert gas atmosphere.

' In Figure l the numeral 11 indicates the crucible inf;

whichthe desired metal or alloy is melted. Preferably,- the crucible is round in cross section and comprises acy lindrical wall 12 and -a bottom 13 ofsomewhat-- greater.

thickness than the wall. provided on the-periphery of-the open end of the crucible.

The crucible 11 is supported within the furnace enclosure A pouring lip 14 is preferably"...:

116 011 a refractory plate 17 carried by a pedestallS and 71 is surrounded "a casing 19, the upper portion of which at least, is formed 'ofel'ectrically nonconductive; refrac tory material such, for example, as mica or asbestos. Within the casing 18, around the crucible 11, there is provided a mass 21 of granularrefractory"materialwhich serves to protect the crucible'fr'om f shock. anda's the'r-I mal insulation therefor. Between the casing 19 andthe" crucible 11 at the top of the mass '21,"there is provided a refractory annulus 22"which p events the granular re fractory material from spilling when thefurnacezis tilted. Spirally wound around "the casing'18' is 'an'electrlcal conductor 23 the ends of which extendoutwardlythrough the enclosure 16' and through the conduit 24 to'make connecj tions'with a suitable source of electric'power (not shown);

At'its top, the'enclosure 16 isprovidedwithjala'rge' opening and a removablecover28"therefor. Extending through agland'32 in thecover 28"is a 'reciprocatable rod 33 to the lower-"end of"which ther'e is attached'a By lowering o'r raising: top or removed therefrom to permit inspection'of the" refractory crucible cover 34; the rod 33'the cover 34 may be placed on' the crucible crucible contents; through thesight'gl'ass 36 andpour ing of the'metal'.

Attachedtothe sidew'all of'the enclosure 16' isa tubular extension '38'withinwhich there is positioned by clamps,"wedges or similar suitable means (not shown) a mold 3?? The outeri'end of the extension 38 is 'pro-' vided 'with"a"'pivoted closure 41 which maybe opened to permit :removal' of the"'rnold. The enclosure'16 is provided with aligned," oppositely disposed trunnions 43 by'which'itis 'pivotally'mounted." The trunnions'are" so'locatedthat 'when'thee'nclosure is rotated in a clock wise direction, as viewed in Figure 1, the contents of the cruciblell'will pour into the mold 39. One'of 'the trunnions 43, as shown,'is tubular and the bore '44'thereof' is connected to avacuum'pump (not shown) by means" of 'which' theinterior ofthe enclosure l6 may' befevacu at ed; There is also 'provided'in the side wallof the en-" closure a nipple 46'through which communicationwith" the'interior of 'the enclosure may be obtained. 7

In carrying out the'pr'ocessof the present invention Example A quantity of blocks of previously sintered titanium having an average Brinell hardness number of 352 were placed in a crucible having the composition CaO-90%. ZrO 7%, TiO 3%. The crucible was then placed in an induction furnace in an' 'evacuated chamber and the titaniumwas melted, remaining at least partially molten for 15 'minutes; The metal wasthen allowed to coolin the crucible. When cool, the "titanium was removed from the crucible;'adherence to the crucible being slight. The

Example 2 A number: of previously sintered titanium blockshav inf'g'" an average Brinelfhar'dness of'352 were placed in atc rucibleiihaving' the composition Ca O85 ZrO infapparatus like that shown in Figure l, the'chargeot high-melting'metal or alloy is placed in the cruciblell and a suitable moldisfplaced in the extensionf38in proper position'to rec'eivemolten metal 'frorn"tl ie"cruciblej The extension38' is thereafter sealedby the closure 41*and'the cover 28 is'secured on'the""enclos ure l 6by v The"enclos'ilre""is "then" evacuated through the bore "44; When the air has been removed from the enclosure the crucible contentsi'naybe suitable means (not shown) heated "by supplying 'high frequency electric currentto the conductor'coil"23'.' When the metal'oralloy has v melted the furnaceie'tilted and'the moltemmetal pours intd'the 1moldy32; Melting-of the metal is "facilitated: bythe "us'e of the"=crucible cover 34 whichreflect's'heat back into the crucible. v I

After 'pouring-'the 'fused metal or alloy into the mold the-furnace-isallowe'd'to cool. The mold may be re moved when -therc-is no longer danger of reaction'be tween the 'metali ingot therein and the air. providing a 'vacuum in' the enclosure 16 it may be de-' sired to use aninert gas such as helium or argon. Such gas may be'admitted through thenipple 46. cases, even when u sing aninert gas atmosphere it may further be desiredtoemploy a "slight sub atmospheric pressure, obtained by use" of a vacuum pump (not shown) connected'to the bore 44, so 'thatanyfumes' given off in the furnace'will be" drawn therefrom and view" of the crucible throughthe sight glass' 29 will'not be-obscured; If desired,"of course,"thefusedmetalbr'i 'alloyimay 'be permitted to solidify in the crucible instead i of pouringit into a mold.-

Thefusion' of titanium in cruciblesformed rrom sev eral compositionsofitheitype "described above"is set forth in the fcllowingex'amples.

Instead of In some 1( %,:TiO "5%" and" fused "an evacuated induction fur" ace; The metalfwa's at least partially molten for 15 rriintitesfjan'd'; was completely molten for more than 3' minutes." The crucible was then cooled and the titanium ing'ot jremoved. No difficulty was experienced in such removal since the 'adhe'rence of the metal to the crucible was low." Inspection 'of the crucible'showed only slight etfosionjthereof. The ingotbbtained had a Brinell hardness of'367 arid an oxygen content of less than 30%} "The c rucible employedin carrying out this fusion ere cast froina'deaired slipcontaining 856 parts by Weight CaCO 91 parts by'weigh't cazro and 53 parts by weightlCaTio suspended in l90 'parts by weight of water containing ll'par't's of. sodium alkyl napth'a lene sulfonate antl'2'par't sof octyl alcohol. It was then dried and fired to"amaximiimtemperature of about 3080 F.

Example 3 .Afnurnb'erof' 'titanium blocks-'like'the ones used 'in ExampIesjLand Z 'werejplac'edin a crucible having the composition CaO -80% ,"Z1"O "l2%,' TiO 8.%. The" crucible containing the metal was then placed 'in an in- I diictio' 'f urriace fandthe metal wa'smelted in 'vacuum., It -was'at"lea'st "partiallymolten"'for"5 minutes and was whollymoltemfor l minutes The metal was allowed to cot' l in the crucible and the resultin'g ingot was then readily removdi; The 'interiorof the crucible showed. I sion: The titanium' ingot' had'a Brinelll hardness 'of 32'! and"an 'oxyg'encontentby analysis of 'approximately.28%.

T eicrucible usedin fusing" thej'titanium in this exwas formed 'by i castingi'a 'de'aired slip containing,

1n mix P1 partsof'watefr, 11 parts sodium alkyl naphthalene suIforiate-QandZ parts offoct'yl alcohol. After drying it w5= fired to' a maximum temperature of about 3050* 1 3" I I Example-*4 having the composition a The metal was completely molten for 3 minutes and}? v. so e? flwd h m ta aha the "same composition and'hardness as that pla'ce in 'aniindu'ction furiiacielo'c'atedt 1n an evacuated enclosure and" the titanium was melted k binder.

tially molten for 6 minutes. After the crucible cooled it was taken from the furnace and the metal ingot was removed. The crucible was in good condition and the titanium ingot obtained was found to have a Brinell hardness of 363 and an oxygen content less than 30%. y The crucible used in carrying out the fusion of the 'example was formed by ramming a moistened grog of the desired composition in substantially the same manner as in Example 1 and was fired to amaximum temperature of about 3050 F.

As heretofore mentioned, the novel process of the present invention is also valuable for fusion of alloys of high-melting metals such as titanium, zirconium and the like. Such use is illustrated in the following examples.

Example 5 A quantity of a chrome-iron titanium alloy containing approximately 95.6% titanium was charged as scrap into a crucible having the composition CaO-80%, ZrO -12% TiO 8%. The crucible was mounted in an induction furnace of the type shown in Figure 1. After first evacuating the system the scrap was melted while feeding argon into the enclosure and maintaining therein an absolute pressure of about 17 inches of mercury. When the charge was molten the furnace was tilted and the contents of the crucible were poured into a cast iron mold. The average Brincll hardness of the scrap charged was 325, while the average hardness of the ingot obtained in the mold was 331. The crucible showed no signs of erosion.

The crucible used in the foregoing example was formed by ramming a mixture of various sizes of particles of electrically fused grog of the composition mentioned above. Before ramming the grog was moistened with a small amount of a solution of an organic temporary After ramming, the crucible was dried and then burned by firing it to a maximum temperature of about 3250 F.

Example 6 Using the same crucible that was used in Eaxmple 5 another charge of the chrome-iron titanium base alloy scrap was fused in substantially the same manner. The titanium alloy ingot from the mold had a Brinell hardness of 350 whereas the average Brinell hardness of the scrap charged was 345. The crucible after use was in excellent condition.

Including the melts of Examples 5 and 6, a total of 7 melts was successfully made in the same crucible and the crucible was still in good condition. This fact shows that attack of the crucible by the molten metal is minimized.

It will be evident from the preceding examples that titanium and titanium alloys may be fused in crucibles, having compositions of the character described and claimed in the copending application above referred to, with only relatively small, and in some cases negligible, increases in hardness. Comparable results may be obtained in the fusion of zirconium, hafnium, and other high-melting reactive metals, and alloys thereof.

As explained above, in carrying out the novel process of the present invention the fused high-melting metal may, if desired, be allowed to soldify in the container or crucible in which it is fused. Thus, the crucible serves as a mold for the metal. It will be obvious, therefore, that if a separate mold is employed into which the molten metal is poured, the mold may be formed of a CaOZrO -TiO refractory of the type with which the present application is concerned. Either ingots or castings of various desired shapes may be thus formed.

In the foregoing description and discussion reference has been made to crucibles, molds, and other refractory bodies formed entirely from a CaOZrO -TiO mix. It will be understood, however, that there may also be used refractory bodies having composite structures. In

such bodies the portions in which the molten, reactive,

terials.

A crucible of the last mentioned type is sho wn in ures 2 and 3 of the accompanying drawings. The crucible 51 comprises an inner, cup-like, container portion 52 having an outwardly projecting annular rim 53 around its open upperend and a concentric, outer, cuplike p01.-

tion 56 in contact with the inner portion 52. The lattei may be formed of a CaOZrO -TiO- refractory such, for example, as any one of the compositions mentioned in Examples 1-4. The outer portion 56 may be formed of any other refractory which is serviceable at the desired temperature of use since, even though it would be readily attacked by the molten metal, it does not come into contact therewith. Among the refractory materials suitable for forming the outer portion 56 are magnesia and zirconia.

Composite crucibles of the type just described may be produced in any suitable and convenient manner. Thus, for example, one or the other of the two portions may be first formed and the other portion then rammed or cast thereon. When only a relatively thin metal-resistant portion or lining is desired, the interior of a crucible of other refractory material may be sprayed, painted, troweled or the like with a slurry or paste of a suitable CaOZrO TiO mix. In some cases the outer portion may be formed of refractory blocks or shapes cemented together by a suitable cement.

It will be understood that the raw materials used in forming crucibles or other containers, such as molds, for use in carrying out the process of this invention need not be chemically pure since minor amounts of normal impurities may be tolerated in such bodies. Indeed, as pointed out in the copending application referred to above, dolomite, which contains substantial amounts of magnesium carbonate along with calcium carbonate, may be used instead of ordinary calcium carbonate as a source of CaO.

In general, crucibles or other containers suitable for carrying out the present invention may have such compositions that the constituent oxides, CaO, ZrO and TiO exclusive of impurities, fall within the following ranges of proportions, CaO% to 39%, ZrO; 7% to 37%, and TiO23% to 24%.

In the foregoing description and the following claims percentages are, unless otherwise indicated, percentages by weight. Further, the term inert atmosphere is intended to include a substantial vacuum as well as an atmosphere of inert gas and the term metal, except where a contrary intention is evident, is meant to include alloys.

1 claim:

1. A process for fusing high-melting reactive metals of the class consisting of titanium and titanium-base alloys without significantly increasing the hardness thereof which comprises heating such a metal in an inert atmosphere in contact with only a refractory consisting essentially of CaO, Zr0 and TiO;.

2. A process for fusing high-melting reactive metals of the class consisting of titanium and titanium-base alloys without significantly increasing the hardness thereof which consists in heating such a metal above its melting point while maintaining it in contact with only an inert atmosphere and a refractory body which consists essentially of 90% to 39% CaO, 7% to 27% ZrO and 3% to 24% TiO 3. A process for fusing high-melting reactive metals of the class consisting of titanium and titanium base alloys without significantly increasing the hardness thereof which comprises heating such a metal in an inert atmosphere and in a container formed essentially of 90% to 39% CaO, 7% to 37% ZrO and 3% to 24% TiO 4. A process for fusing high-melting reactive metals of the class consisting of titanium and titanium-base a1 loyswithout significantly increasing the hardness thereof which comprisespla'cing such a metalin a container having a composition, exclusive of impurities, of from 90% to 39% C210, 7% to 37% Z10; and 3% to 24% TiOg, and heatingsaid metal in an inert atmosphere. 5

' References Cited..in.the file of this patent UNITED STATES PATENTS 2,205,854 K'roll June 25, 1940 10 8 Wainer Jnne 18, 1946 Wainer June 18, 1946 Wainer' Oct. 26 1948 Woodcocket a1. Feb. 13, 1951 Hathaway III May 18, 1954 Urban July 20, 1954 FOREIGN PATENTS Great Britain Oct. 31, 1947 Great Britain Oct. 24, 1951' 

1. A PROCESS FOR FUSING HIGH-MELTING REACTIVE METALS OF THE CLASS CONSISTING OF TITANIUM AND TITANIUM-BASE ALLOYS WITHOUT SIGNIFICANTLY INCRAEASING THE HARDNESS THEREOF WHICH COMPRISES HEATING SUCH A METAL IN AN INERT ATMOSPHERE IN CONTACT WITH ONLY A REFRACTORY CONSISTING ESSENTIALLY OF CAO, ZRO2 AND TIO2, 